The authors report a case of bilateral chronic subdural hematoma in a 25-year-old woman who had occipital and neck pain. Magnetic resonance imaging revealed progressive caudal descent of the cerebellar tonsils (acquired Chiari I malformation) and a large eccentric syrinx in the spinal cord from the C3-T7 levels. Spontaneous disappearance of the chronic subdural hematomas resulted in radiographic resolution of both lesions, as well as clinical improvement. Theories of syringomyelia formation, the relationship to acquired Chiari I malformation, and the implications of this case are discussed.